Home Cold War Era ‘Blackbird’s Top Speed was Officially Mach 3.2 but the SR-71 was Much Faster Than That,” former Skunk Works Engineer Says

‘Blackbird’s Top Speed was Officially Mach 3.2 but the SR-71 was Much Faster Than That,” former Skunk Works Engineer Says

by Dario Leone
‘Blackbird’s Top Speed was Officially Mach 3.2 but the SR-71 was Much Faster Than That,” former Skunk Works Engineer Says

‘Shul’s narrative of flight at or above Mach 3.5 is so far the most detailed evidence available of SR-71 top speeds,’ Tim Yarrow, Electrical Engineer at Lockheed’s Skunk Works from 1974-1994

The SR-71 reconnaissance aircraft was the world’s fastest jet-propelled aircraft and the most advanced member of the Blackbird family developed by Lockheed Aircraft Corporation’s clandestine “Skunk Works” division. The SR-71 accrued nearly 2,800 hours of flight time during its 24 years of service with the U.S. Air Force. The aircraft was designed to fly deep into hostile territory, avoiding interception with its tremendous speed and high altitude.

During its operational lifetime, the SR-71 provided intelligence about the Yom Kippur War in 1973, the Israeli invasion of Lebanon in 1982, the US raid on Libya in 1986 and the revelation of Iranian Silkworm missile batteries in 1987. The U.S. Air Force ceased SR-71 operations in January 1990.

The Blackbird was designed to cruise at “Mach 3+,” just over three times the speed of sound or more than 2,200 miles per hour and at altitudes up to 85,000 feet. 

Now, as we have previously explained, when talking about SR-71 probably the most frequently asked Blackbird question is-how high and how fast does it really fly?

‘Blackbird’s Top Speed was Officially Mach 3.2 but the SR-71 was Much Faster Than That,” former Skunk Works Engineer Says

Tim Yarrow an aviation Research and Analysis expert was an Electrical Engineer at Skunk Works from 1974-1994, recalls:

‘Faster than widely published. Blackbird’s cruise speed was officially Mach 3.2…but there’s MORE.

‘Blackbird pilot Brian Shul described a surveillance mission over Tripoli, Libya, in April 1986 [CLICK HERE to read how Brian Shul’s SR-71 outran Gaddafi’s SAMs during the famed BDA flight of Libya in support of Operation El Dorado Canyon]. Photographic evidence was required for bomb damage assessment (BDA) following a U.S. bombing run in retaliation for the Qaddafi-sponsored terrorist attack on a Berlin disco. Satellites were not available to immediately task over Tripoli for BDA. This was a surveillance mission for which the SR-71 was designed, albeit a quarter-century ago.

‘The difference was that by 1986 missile capability had significantly improved. And Libya had them. As the Blackbird crossed the “Line of Death” into Libyan territory, Shul’s co-pilot warned of ground-based missile launches, Russian SAMs they guessed, capable of Mach 5 flight. Those scary little f***ers were probably the only thing a Blackbird pilot feared.

‘Remember: the only defenses a Blackbird had was speed and altitude.

‘Blackbird’s Top Speed was Officially Mach 3.2 but the SR-71 was Much Faster Than That,” former Skunk Works Engineer Says

‘Still, flying at Mach 3.2 at 80,000 feet is a significant head-start.

‘Shul relates that he and his co-pilot calculated they could *just* make their turn over Libya to accomplish their surveillance objectives, but only if they increased speed. Because the Blackbird surveillance missions are planned to the second with regard to speed, altitude, and fuel load, a speed excursion above Mach 3.2 was a pilot safety decision completely outside of pre-flight planning.

‘However, on this day the jet performed flawlessly and delivered the speed asked of it.

‘The plane responded with smooth, confident power, delivering speed that was previously the subject of much theory and conjecture.’

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‘Shul narrates in his book Sled Driver that as more missile launches were detected with the Mach easing to 3.5, he pushed the throttles full forward against the stops.

‘Shul continued a 500-Feet per Minute climb (one-sixth of one degree pitch-up…do the math) while accelerating, to the turn-point. The engines ran “relatively cool”.’

Here’s an excerpt From Major Brian Shul’s book Sled Driver: ‘After several agonizingly long seconds, Co-pilot Walter suggested, ‘You might want to pull it back’. It was then that I noticed……I still had the throttles full forward. The plane was flying a mile every 1.6 seconds, well above our Mach 3.2 limit. It was the fastest we would ever fly.’

SR-71 Print
This print is available in multiple sizes from AircraftProfilePrints.com – CLICK HERE TO GET YOURS. SR-71A Blackbird 61-7972 “Skunkworks”

Tim Yarrow continues:

‘They took the photos, made the turn, and only when the blue Mediterranean was safely outside their window, he backed off the throttle.

‘To be sure, this was no hopped-up model of the SR-71. This was the standard Blackbird, maintained and flown in top form.

‘So, I presume there will continue much discussion of just how fast the plane could fly……and if it was much faster than Mach 3.5, it is a well-kept secret, possibly for the national security reasons.

‘Shul’s narrative of flight at or above Mach 3.5 is so far the most detailed evidence available of SR-71 top speeds.’

If you want a little more, Tim Yarrow explains how SR-71’s Pratt & Whitney J58 engine works.

‘At speed, the J58 engines operate more like a RAM jet than a turbo jet. It operates more efficiently the faster it flies.

‘The catch is that inlet and exhaust temperatures must be monitored closely to stay within engine design limits. In this mode, the engine was gulping more than 100,000 cubic feet of air every second.

‘The engine spikes retract 26 inches into the nacelles, and all engine inlets doors are closed except for the main inlet and exhaust.

‘J58 engine inlet and nacelle, showing the shock spike extended fully forward, the position for engine start, take-off, and cruise up to Mach 1.5. At speeds above Mach 1.5, the spike was incrementally pulled back into the nacelle 1.6″ per 0.1 Mach increase until retracted a full 26 inches at Mach 3.2.
This was done to capture the “normal” shock wave in the engine nacelle inlet and slow the air for subsonic delivery into the engine compressor stages.

‘This is the much-storied ram effect achieved at and above Mach 3.2. And consider that this is 1950s technology!’

SR-71 Model
This model is available from AirModels – CLICK HERE TO GET YOURS.

Photo credit: U.S. Air Force

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1 comment

mickrussom Nov 2 2019 - 10:25 PM

doubtful it was much more than 3.2. the reason is the cone had to move to adjust the shockwave. the cone was in its furthest position at 3.2. any faster than mach 3.2 and the shockwaves would go into the inlets and cause an unstart. unstarts caused the breakup of the sr-71. so while the engines could potentially push the airframe faster the shockwaves produced would increase the chance of a catastrophic unstart.

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Welcome to The Aviation Geek Club, your new stopover aviation place. Launched in 2016 by Dario Leone, an Italian lifelong - aviation geek, this blog is the right place where you can share your passion and meet other aviation enthusiasts from all over the world.

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